The present invention relates to a method and apparatus for making a rod from powdered metal, and more particularly to a new and novel method for continuously forming the rod from powdered metal and to a new and novel apparatus for carrying out the method.
One method and an apparatus for continuously forming rod from powdered metal is described in U.S. Pat. 2,097,502 granted Nov. 2, 1937. This method comprises generally the compaction and compression of successive lengths of rod in a mold including die members which are separable to release pressure radially applied by the die members and thereby to release a length of rod from the mold. The rod thus formed is subsequently sintered.
By the present invention it is proposed to provide an improved method for continuously forming a bar from a powdered metal wherein successive separate quantities of powdered metal are axially compacted by compacting means axially moveable in a unitary die having a cavity of fixed cross-sectional area into bar segments bonded to each other to form a green compact bar. The green compact bar is incrementally forced out of the die such that a length thereof is frictionally retained within the die to serve as a stopper against which a succeeding quantity of powdered metal is compacted. The frictional resistance force between the cavity wall and the length of the bar defining the stopper is measured. This measurement is used to determine if the frictional resistance force corresponds to the compacting force required to compact the quantity of powdered metal into a bar segment having desired physical characteristics. If the frictional force deviates from the required force, the length of travel of the compacting means and the volume of powdered metal are varied relative to each other until the measured resisting force corresponds to the required compacting force whereby the powdered metal is compacted into a bar segment having the desired physical characteristics.
In accordance with the present invention the compaction is accomplished by a punch which is reciprocable within the die cavity. The required frictional force is maintained by controlling the length of travel of the punch in the cavity so that the quantity of powdered metal is compacted to provide a green compact rod of substantially uniform physical characteristics along its length.
The green compact rod formed in the continuous manner as described above is then sintered to improve the physical characteristics after emerging from the die. Preferably the sintering is performed by induction heating means.
After sintering the rod may also be swagged or otherwise hot worked to further increase the density thereof.
Further features of the invention will hereinafter appear.